Filling machines for filling pasty masses, in particular for filling sausage casings, are already known from prior art. Filling machines generally comprise a hopper into which a pasty mass is filled, and from which the pasty mass is via a delivery pump conveyed, for example, into a stuffing tube, from where the pasty mass is then ejected into a sausage casing. Individual portions are produced with appropriate filling machines and their weight should preferably be very accurate. The weight accuracy of a filling machine, in particular a vacuum filling machine, depends on numerous factors. They include inter alia the variances of the variables specific to the environment, the input product, the output product, machines and processes. In particular the ambient and product temperatures, the viscosity of the mass to be filled, the stuffing tube diameter, the pump geometry, the filling speed etc. are of significance.
The aforementioned systematic influences can be compensated at least in part by appropriate countermeasures. Correcting portion weight fluctuations is in practice usually effected by readjustment of the portion weight or volume that is set at the pump of the filling machine.
However, so-called random errors additionally occur in practice. They are much more difficult to control or correct and therefore contribute significantly to unsatisfactory weight accuracy of the filled portions over a prolonged period of time. They include primarily uncontrollable flow processes within the pump due to pressure fluctuations in the outlet region of the rotary vane pump. In rotary vane pumps, the pasty mass, which is by the ambient air pressure pressed from the hopper into the conveying mechanism, is in the vane chamber conveyed toward the outlet, where the volume of the vane chambers decreases towards the outlet such that the pasty mass is compressed and the pressure in the pressure region increases toward the outlet. It is thereby possible that a pressure equalization flow, due to pressure differences between the pressure and the suction region, occurs from the pressure region of the rotary vane pump to the suction region, whereby weight inaccuracies arise (see e.g. also FIG. 6 in which the pressure region is denoted by 32 and the suction region by 31). Pressure equalization flows between individual chambers due to small gaps can also occur.
The main problem of the portion weight compensation method lies in the fact that this is a reactive iteration method, i.e. the achievable portion weight accuracy is often unsatisfactory due to constantly drifting actual values—at the same time requiring increased adjustment work.
In order to obtain increased portion accuracy, solutions have already been attempted in which two dosing pumps are disposed one behind the other, i.e. that actually two vacuum filling machines must be provided, one of which comprises a hopper. However, this leads to a number of drawbacks, such as e.g.—high cost,—increased number of wearing parts,—poor cost-efficiency,—increased likelihood of failure,—increased cleaning effort,—increased space requirement,—increased energy consumption,—reduced flexibility because the system is bulky and can not be retooled in a short period of time.